The HIV-1 envelope contains multiply overlapping (and redundant) mechanisms of humoral immune defence. These including glycan shielding, conformational masking, and immunodominant decoys with variable loops. Although explored extensively, many of these mechanisms are still only partially understood. We are using structure-based methods to define them further. In addition, we are examining the fusion glycoprotein from respiratory syncytial virus, to understand its mechanisms of humoral evasion.